Heat treatment of steel rails



:Fatented Jan. 17, 1933 PATENT. OFFICE JoHN BRUNNER, F oHIGAGO, ILLINOIS HEAT TREATMENT OF STEEL RAILS No Drawing. Original application filed October 22,1931, Serial No. 570,496. Divided and this application filed June 11, 1932.

This invention relates to metallurgy and more particularly to the heat treatment of metals and alloys to improve the qualities thereof and still more particularly to the heat treatment of steel rails. This application is a divisional application of application Serial No. 570,496 filed October 22, 1931 entitled Heat treatment of steel rails.

This invention is substantially an improvement of the invention set forth in my U.. S. Patent No. 1,277,37 2 issued September 3, 1918.

The process of U. S. Patent No. 1,27 7,372 substantially comprises a method of heat treating steel rails to obtain therein a more uniform and fine grain structure and a better surface than had heretofore been obtainable. The method substantially comprises rollmg the rail to a section larger than the desired finished section; cooling the rail to temperatures below the thermal critical range; re-

heating the rail to temperatures above the thermal critical temperatures (approximately 800 C.); rolling the rail to the desired finished section; and slowly cooling the rail to room temperatures. This method produced a finished rail havinga fine grain structure which imparted thereto great toughness. The rail product, however, did not possess sufficient surface hardness to make it resistantto severe service conditions.

One of the objects of the present invention is to increase the surface hardness of the rail product of my prior invention.

Another object of the present invention is to provide heat-treating methods whereby the surface hardness of a steel rail may be materially increased at its ends where the greatest abrasion and battering takes place in service under the rolling loads of motive power and transportation equipment. I

Another object of the present invention is to provide a steel rail having an interior of relatively high ductility throughout the entire length of the rail and an exterior of relatively high hardness at the ends of the rail.

Another object of the present invention is to improve and facilitate the manufacture of steel rails.

Other objects and advantages will be ap- Serial No. 616,761.

parent as the invention is more fully disclosed.-

In accordance with the objects of the prescut invention I have found that I may impart a relatively high surface hardness to the relatively tough fine grain structure in the rail prepared in accordance with the invention of my prior patent, thereby materially increasing the resistance of the rail to service conditions, by subjecting the rail to certain heat-treating methods. The heat-treating method substantially comprises the following steps:

At the conclusion of the final rolling operation the finished rail is cooled totemperatures approximating 300 0., and is then reheated to relatively uniform temperatures which are slightly above the thermo-critical range of the specific composition of steel used therein and then cooling the head of the rail at and near its ends in a quenching medium until the surface temperature of this part of the rail has been lowered at least partially through the blue-heat range (approximately 288 C. to 816 C.) but to temperatures not lower than 200 C.; thereafter the entire rail is quenched, preferably in oil, to temperatures approximating but not less than about 250 0., and again heated to temperatures above 300 C. but below the thermal critical range for a determined time interval and therafter cooled slowly in air to atmospheric temperatures.

In this manner I first effect a refinement of the internal grain structure of the rail, increasing its uniformity and toughness, and then a hardening of the surface of the head thereof at and near its ends, thereby obtaining a. desired amount of external surface hardness of the rail ends to resist abrasion and battering of the rail ends in the track in service, and a mild hardening of the surfaces intermediate the ends, followed by an annealing or tempering to remove internal stresses and strains incident. to the hardening operation.

As a specific embodiment of the practice of this invention I Will disclose the method as applied to a steel rail composition comprising carbon .40 to 85%; manganese .40 to ture if not less than 300 C. and is again rethe per cent reduction in area remaining is only that which is suflicient to obtain an accurate section of the rail.

The cooled rail is then reheated to rela tively uniform temperatures approximating 800 C. and is thereafter rolled to the desired finished section. The finished rail is thereafter allowed to cool to an average temperaheated to relatively uniform temperatures approximating 800 (3., and from these temperatures is quenched on the head at and near both ends of the rail until the surface temperatures of this part of the rail has been lowered partially through the blue-heat range but not lower than 200 C. After the ends have been quenched the entire rail is quenched preferably in oil until the surface temperatures of the part of the rail between the pre-quenched ends approximate but are not less than about 250 C. The quenched rail is then transferred into a furnace and heated to minimum temperatures above 300 C. but below the thermal critical range (approximately 600 C.) after a predetermined time interval approximating from one-half to two hours, following which it is allowed to coolslowly in the air to atmospheric temperatures.

The rail product thus produc'ed'will be found to have retained the fine grain struc ture of my prior patent with an exterior sur-. face on top of the head at the end of the rail of greater hardness than heretofore obtainable by cold workingmeans alone. For example, the finished rail product of my prior patent will have a surface hardness of ap proximately 250-280, as measured on the Brinell scale. The finished rail product of the specific embodiment of the present invention will have a surface hardness of the head at and near the ends of the rail approximating from 340 to 410, depending on the section and intended service of the heat treated rail.

The exact cooling temperatures and the time intervals of cooling may be widely varied depending upon the composition of the steel, the finished hardness desired, and upon the internal grain structure desired in the rail.

While I have disclosed as a specific embodiment the steps of rolling the rail to a section larger than the desired finished section, cool- Whereas, also the above invention has been disclosed with particularity as regards to its application to a specific rail composition, it

is. apparent that with modifications in the steel compostion, modifications in the heat treating process may be made accordingly.

Such modifications and departures are contemplated as may following claims:

What I claim is:

1. The method of heat treating steel rails to increase the surface hardness thereof and especially on the head at and near its ends, which comprises'heating the rail to temperatures approximating but above the thermal critical range, quenching the head of the rail at and near its ends until the surface temperatures of the head at and near its ends approximate but are not less than 200, C., then quenching the entire rail until the surface temperatures thereof between the prequenched ends approximate but are not less than 250 0., reheating the rail to temperatures higher than the quenching. temperatures but below the thermal critical temperatures and thereafter slowly cooling to atmospheric temperatures. A

2. The method of hardening the surface of steel rails having an approximate composition of carbon .40 to .85%; manganese .40 to 1.60%; phosphorus, not over .08%; sulphur, not over .08%; silicon, not 1.50% which comprises heating the rail to temperatures approximatin but above the thermal critical range, quenchmg the head of the rail at and near its ends until the surface temperature of the head at and near its ends aproximate but are not less than 200 (3., then quenching the entire rail until the surface temperatures thereof between the prequenched ends approximate but are not less than 250 0., an nealing the rail at temperatures approximatingv 600 (-1, and thereafter slowly cooling to room temperatures.

3. The method of hardening the surface of steel rails having an approximate-composition of carbon .40 to .8570; manganese .40 to 1.60%; phosphorus, not over 08%; sulphur, not over .08% silicon, not over 1.50% which comprises heating the rail to temperatures approximating 800 C., quenching the head of the rail at and near its ends until the surface temperatures of the head at and fall within the scope of the 4. The method of hardenlng the surface of steelrails having an approximate composi-.

tion of carbon .40 to .85; manganese .40 to 1.60%; phosphorus, not over .08%; sulphur, not over 08% silicon, not over 1.50% which comprises heating the rail to temperatures approximating 800 0., quenching the head of the rail at and near its ends in water until the surface temperatures of the head at and near its ends approximate but are not less than 200 0., then quenching the entire rail until the surface temperatures of the part of the rail between the ends which has not been pre-quenched approximate but are not less than 250 0., annealing the rail for a predetermined time interval at temperatures approximating 600 0., and thereafter slowly cooling to room temperatures.

5. The method of forming steel rails which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a section larger than the desired finished rail section, cooling to temperatures below the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to temperatures below the thermal critical range but above 300 0.,

reheating'to temperatures approximating but above the thermal critical range, quenching the head of the rail at and near its ends until the surface temperatures of the head at and near its ends lie within the blue-heat range but above about 200 0., ,then quenching the entire rail until the surface temperatures between the pro-quenched ends lie within the blue-heat range but above 250 0.,, reheating to temperatures above 300 0. butbelow the thermal critical range and thereafter cooling slowly to room temperatures.

6. The method of forming steel rails hav-- ing an approximate composition of carbon .40 to manganese .40'to 1.60%; phosphorus, not over 08%; sulphur, not over 08%; silicon, not ovef 1.50%; which comprises heating the rail ingot or billet to rolling temperatures abo-vethe thermal critical range, rolling to a section larger than the desired finished section, cooling to temperatures lower than the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to temperatures below the thermal critical range, but above of the head at and near its ends lie within the blue-heat range but above about 200 0., then quenching the entire rail until the surface temperaturesof the part of the rail between the pre-quenched ends lie within the blue-heat range but above about 250 0., annealing the rail at temperatures approximating 600 0., and thereafter slowly cooling to atmospheric temperatures.

7. The method of forming steel rails having an approximate composition of carbon .40 to 85%; manganese .40 to 1.60%; phosphorus, not over 08%; sulphur, not over 08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a section larger than the desired finished section, cooling to temperatures lower than the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to' temperatures below the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, quenching the head of the rail at in the blue-heat range but above about 250 0., annealing the rail at temperatures approximating 600 0. for a predetermined time interval, and thereafter slowly cooling to atmospheric temperatures.

8. The method of forming steel rails having an approximate composition of carbon .40 to 85%; manganese .40 to 1.60%; phosphorus, not over 08%; sulphur, not over 08%; silicon not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling to a section larger than the desired finished section, cooling to temperatures lower than the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, rolling to the desired finished section, cooling to temperatures below the thermal critical range, but above about 300 0., reheating to temperatures approximating but above the thermal critical range, quenching the head of the rail at and tween the pre-quenched ends lie within the blue-heat range but above about 250. (1., annealing the rail at temperatures approximating 600 (1. for approximately one-half to two hours, and thereafter slowly cooling'to 300 (1., reheating the rail to temperatures approximating but above the thermalcritical range, quenching the head of the raiLat and near its ends until the surface temperatures of the head at and near its ends approximate but are above 200 (1., then quenching the entire rail until the surface temperatures of the part of the rail between the prequenchled ends approximate but are above 250 (1., annealing to temperatures above about 300 (1. but below the thermal critical range and thereafter slowly cooling to room temperatures.

7 10. The method of forming steel rails from a rail ingot or billet having a composition of carbon .40 to .8570; manganese .40 to 1.60%; phosphorus, not over .0870; sulphur, not over .08% silicon, not over 1.50% which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling the rail to the desiredfinished section, cooling the rail to temperatures below the thermal critical range but above about 300 (1., reheating to temperatures approximating but above the thermal critical range, quenching the head of-the rail at and near its ends until the surface temperatures of the head at and near its ends approximate but are above 250 (1., then quenching the entire rail until the surface temperatures between the pre-quenched ends approximate but are above 250 (1., annealing the railto temperatures above 300 C. but less than the thermal critical range and thereafter slowly I cooling to atmospheric temperatures.

11. The method of forming steel railsfrom a rail ingot or billet having a composition of carbon .40 to .85% ;'manganese .40 to 1.60%; phosphorus, not over 08% sulphur, not over .08%; silicon, not over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range, rolling the rail to the desired finished section, cooling the rail to temperatures below the thermal critical range but above about 300 (1., reheating to temperatures approximating but above the thermal critical range, quenching the head of the rail at and near its ends until the surface temperatures of the head at and near its ends approximate but are above about 250 (1., then quenching the entire rail until the surface temperatures between the pre-quenchedends approximate but are above 250 (1., annealing the rail to term peratures above 300 (1., but not less than the thermal critical range for a predetermined time interval and thereafter slowly cooling to atmospheric temperatures.

12. The method of forming steel rails from a rail ingot or billet having a composition approximating carbon .40 to .85%; manganese .40 to 1.60%; phosphorus, not over .08%; sulphur, not over 08%; silicon, not

over 1.50%; which comprises heating the rail ingot or billet to rolling temperatures above the thermal critical range,'rolling the rail to the desired finished section, cooling the rail to temperatures below the thermal critical range but above about 300 (1., reheating to temperatures approximating but above the thermal critical range, quenching the head of the rail at and near its ends until the surface temperatures of the head at and near its ends approximate but are above about 250 (1., then quenching the entire rail until the surface temperatures of the rail between the pre-quenched ends approximate but are above about 250 (1., annealing the rail to temperatures above 300 (1., but less than the thermal critical range for approximately one-half to two hours, and thereafter slowly cooling to atmospheric temperatures.

13. The method of treating steel rails to harden the same which comprises quenching the head of the rail at and near its ends from v a temperature above the critical temperature to a temperature approximating but not less than 200 (1. and then quenching the entire rail until the surface temperature thereof between the prequenched ends approximate but are not less than 250 (1., then reheating the rail to temperatures higher than the quenching temperatures but below the critical temperature and thereafter slowly cooling to room temperatures.

In witness whereof, I have hereunto signed my name.

JOHN BRUNNER. 

